This invention relates to (i) a novel cyclic acetal compound or a mixture of cyclic acetal compounds useful as a monomer to form a polymer, (ii) a polymer comprising specific recurring units, (iii) a resist composition comprising the polymer as a base resin, suited in a micropatterning process, and (iv) a patterning process using the resist composition.
While a number of recent efforts are being made to achieve a finer pattern rule in the drive for higher integration and operating speeds in LSI devices, deep-ultraviolet lithography is thought to hold particular promise as the next generation in microfabrication technology. In particular, photolithography using a KrF or ArF excimer laser as the light source is strongly desired to reach the practical level as the micropatterning technique capable of achieving a feature size of 0.3 xcexcm or less.
For resist materials for use with a KrF excimer lasers, polyhydroxystyrene having a practical level of transmittance and etching resistance is, in fact, a standard base resin. For resist materials for use with ArF excimer lasers, polyacrylic or polymethacrylic acid derivatives and polymers containing aliphatic cyclic compounds in the backbone are under investigation. All these polymers have advantages and disadvantages, and none of them have been established as the standard base resin.
More particularly, resist compositions using derivatives of polyacrylic or polymethacrylic acid have the advantages of high reactivity of acid-decomposable groups and good substrate adhesion and give relatively satisfactory results with respect to sensitivity and resolution, but have extremely low etching resistance and are impractical because the resin backbone is weak. On the other hand, resist compositions using polymers containing alicyclic compounds in their backbone have a practically acceptable level of etching resistance because the resin backbone is robust, but are very low in sensitivity and resolution because the reactivity of acid-decomposable protective groups is extremely low as compared with those on the acrylic polymers. Since the backbone of the resin is too robust, substrate adhesion is poor. These compositions are thus impractical as well. While a finer pattern rule is being demanded, there is a need to have a resist material which is satisfactory in sensitivity, resolution, and etching resistance.
Therefore, an object of the present invention is to provide (i) a novel cyclic acetal compound and a mixture of cyclic acetal compounds useful as a monomer, (ii) a polymer having improved reactivity, robustness and substrate adhesion, (iii) a resist composition comprising the polymer as a base resin, which is improved in adhesion and transparency when processed by photolithography using light having a wavelength of less than 300 nm, especially ArF excimer laser light and which has a higher resolution and etching resistance than conventional resist compositions, and (iv) a patterning process using the resist composition.
The inventors have found that novel cyclic acetal compounds of the formula (i), or mixtures of a 5-membered ring acetal compound of the formula (i) and a 6-membered ring acetal compound of the formula (v), all shown below, are easily produced in high yields by the method to be described later; that polymers obtained from the cyclic acetal compounds or the mixtures of cyclic acetal compounds are highly transparent at the exposure wavelength of an excimer laser; and that a resist composition using the polymer as a base resin is improved in adhesion to substrates. It has also been found that novel polymers comprising recurring units of the formula (1-1) or (1-2) and having a weight average molecular weight of 1,000 to 500,000, which are produced from the cyclic acetal compounds or the mixtures of cyclic acetal compounds by the method to be described later, have improved reactivity, robustness or rigidity and substrate adhesion; that a resist composition comprising the polymer as the base resin has a high resolution and etching resistance; and that this resist composition lends itself to precise micropatterning.
In a first aspect, the invention provides a cyclic acetal compound of the following general formula (i), and especially formula (ii). 
Herein k is 0 or 1 and n is an integer from 0 to 6.
The invention also provides a cyclic acetal compound mixture comprising a 5-membered ring acetal compound of the general formula (i) and a 6-membered ring acetal compound of the general formula (v), and especially a 5-membered ring acetal compound of the general formula (ii) and a 6-membered ring acetal compound of the general formula (vi). 
Herein k and n are defined above. 
In a second aspect, the invention provides a polymer comprising recurring units of the following general formula (1-1) or (1-2) and having a weight average molecular weight of 1,000 to 500,000.
Herein R is hydrogen or methyl, k and n are as defined above.
In a preferred embodiment, the polymer further includes recurring units of the following general formula (1xe2x80x2-1) or (1xe2x80x2-2). 
Herein R, k and n are as defined above.
In another preferred embodiment, the polymer includes, in addition to the recurring units of formula (1-1), recurring units of the following general formula (2-1). 
Herein k is as defined above; R1 is hydrogen, methyl or CH2CO2R3; R2 is hydrogen, methyl or CO2R3; R3 is a straight, branched or cyclic alkyl group of 1 to 15 carbon atoms; R4 is an acid labile group; R5 is selected from the class consisting of a halogen atom, a hydroxyl group, a straight, branched or cyclic alkoxy, acyloxy, alkoxycarbonyloxy or alkylsulfonyloxy group of 1 to 15 carbon atoms, and a straight, branched or cyclic alkoxyalkoxy group of 2 to 15 carbon atoms, in which some or all of the hydrogen atoms on constituent carbon atoms may be substituted with halogen atoms; Z is a single bond or a straight, branched or cyclic (h+2)-valent hydrocarbon group of 1 to 5 carbon atoms, in which at least one methylene may be substituted with oxygen to form a chain-like or cyclic ether or two hydrogen atoms on a common carbon may be substituted with oxygen to form a ketone; and h is 0, 1 or 2.
In a further preferred embodiment, the polymer includes, in addition to the recurring units of formula (1-1), recurring units of the following general formulae (2-1) and (3). 
Herein k, h and R1 to R5 are as defined above.
In a still further preferred embodiment, the polymer includes, in addition to the recurring units of formula (1-1), recurring units of the following general formula (2-1) and/or recurring units of the following general formula (4), and recurring units of the following general formula (3). 
Herein k, h and R1 to R5 are as defined above.
The polymer of any of the preferred embodiment may further include recurring units of the general formula (11-1).
In an alternative embodiment, the polymer includes, in addition to the recurring units of formula (1-2), recurring units of the following general formula (2-2). 
Herein k, h and R1 to R5 are as defined above. The polymer may further include recurring units of the general formula (1xe2x80x2-2).
In a third aspect, the invention provides a resist composition comprising the polymer defined above.
In a fourth aspect, the invention provides a process for forming a resist pattern comprising the steps of applying the resist composition onto a substrate to form a coating; heat treating the coating and then exposing it to high-energy radiation or electron beams through a photo mask; and optionally heat treating the exposed coating and developing it with a developer.
The polymers comprising recurring units of formula (1-1) or (1-2) have high rigidity since bridged aliphatic rings are incorporated in the backbone. They show improved substrate adhesion since they have on a side chain a five or six-membered ring cyclic acetal structure with a high polarity in addition to an ester structure and are thus rich in oxygen functional groups. A spacer of appropriate length introduced between the cyclic acetal structure-bearing ester portion and the rigid backbone serves to properly alleviate the rigidity which has been excessive in the prior art. Since the cyclic acetal structure moiety is spaced apart from the backbone, it can act more positively as a polar group. These factors cooperate to develop a substrate adhesion force surpassing the prior art compositions. Although low reactivity is left outstanding in the prior art, the spacer introduced allows the acid generated to diffuse smoothly, thereby improving reactivity and as an accompanying benefit, achieving a reduction of line edge roughness. Therefore, a resist composition using the polymer as a base resin satisfies all the performance factors of sensitivity, resolution and etch resistance and is very useful in forming micropatterns.
The cyclic acetal compounds of the invention has the following general formula (i): 
wherein k is 0 or 1 and n is an integer from 0 to 6.
Illustrative, non-limiting, examples of the cyclic acetal compounds are given below. 
In another embodiment of the invention, a cyclic acetal compound mixture is provided comprising a 5-membered ring acetal compound of the general formula (i) and a 6-membered ring acetal compound of the general formula (v). 
Herein k is 0 or 1 and n is an integer from 0 to 6.
Illustrative examples of the 6-membered ring acetal compound of formula (v) correspond to the above-illustrated examples of the 5-membered ring acetal compound of formula (i) in which the group (A) is replaced by the group (B) as shown below. 
In resist polymers prepared from these compounds as monomers, the cyclic acetal moiety which is regarded to be a polar group for developing adhesion is spaced apart from the polymer backbone by a linker (represented by xe2x80x94(CH2)nCO2CH2xe2x80x94 in formula (i)), so that satisfactory substrate adhesion is developed. Using monomers in which k and n have optimum values, the overall polymer is properly adjusted in fat solubility and thus controlled in dissolution characteristics.
The cyclic acetal compounds or mixtures thereof according to the invention can be prepared, for example, by either of the following two methods, although the preparation method is not limited thereto.
Since glycerol formal used as the starting reactant in either of the methods contains a 5-membered ring acetal structure (iii) and an isomer, 6-membered ring acetal structure (iv), the actually obtained cyclic acetal product is a mixture of a 5-membered ring acetal compound (i) and a 6-membered ring acetal compound (v). For the sake of brevity, the following description is made on the assumption that the glycerol formal consists solely of a 5-membered ring structure (iii), that is, the 5-membered ring structure is a representative. 
Herein k is 0 or 1 and n is an integer from 0 to 6.
In the first method, the end cyclic acetal compound (i) is synthesized by esterifying glycerol formal (iii) with an acid halide (vii) in the presence of a base. 
Herein X is a halogen atom, k is 0 or 1, and n is an integer from 0 to 6.
An appropriate amount of the acid halide (vii) used is 0.5 to 2.0 mol, especially 0.9 to 1.1 mol per mol of the glycerol formal (iii). The reaction is effected in the presence of a base and in a solvent or without solvent. Preferred examples of the base used herein include tertiary amines such as triethylamine, diethylisopropylamine, pyridine, N,N-dimethylaniline and 4-dimethylaminopyridine, alone or in admixture of any. The base is used in an amount of 1.0 to 20 mol. preferably 1.0 to 2.0 mol per mol of the acid halide (vii). The base itself may serve as the solvent although a suitable solvent may be used which is selected from among ethers such as tetrahydrofuran, diethyl ether, di-n-butyl ether and 1,4-dioxane, hydrocarbons such as n-hexane, n-heptane, benzene, toluene, xylene and cumene, and chlorinated solvents such as methylene chloride, chloroform and dichloroethylene. The reaction temperature is from xe2x88x9250xc2x0 C. to 80xc2x0 C., preferably 0xc2x0 C. to 50xc2x0 C. The reaction time is desirably determined by monitoring the reaction until the completion by gas chromatography (GC) or silica gel thin-layer chromatography (TLC) because higher yields are expectable. The reaction time is usually about 0.5 to about 20 hours. From the reaction mixture, the end cyclic acetal compound (i) is obtained by a conventional aqueous work-up step. If necessary, the end compound (i) is purified by any conventional technique such as distillation or chromatography.
In the second method, the end cyclic acetal compound (i) is synthesized from glycerol formal (iii) and an ester compound (viii). 
Herein R is an alkyl such as methyl or ethyl, k is 0 or 1, and n is an integer from 0 to 6.
When these reactants are used, the end compound (i) is obtained through transesterification reaction using a catalyst. The reaction may be effected in a solvent or without solvent. During the reaction, the alcohol (ROH) formed is preferably distilled off because of advantages including increased yields, reduced reaction time, and saving of the glycerol formal (iii) amount. An appropriate amount of glycerol formal (iii) used is 0.5 to 5.0 mol, especially 1.0 to 1.5 mol per mol of the ester compound (viii). The transesterification catalysts used include, though are not limited thereto, organic amines such as triethylamine, 1,8-diazabicyclo[5.4.0]-7-undecene and 4-dimethylaminopyridine, inorganic bases such as sodium hydroxide, potassium carbonate and sodium carbonate, and metal alkoxides such as sodium methoxide, potassium t-butoxide, magnesium ethoxide, and titanium (IV) methoxide. An appropriate amount of the transesterification catalyst used is 0.001 to 5.0 mol, especially 0.001 to 0.1 mol per mol of the ester compound (viii). The solvent is selected from among ethers such as tetrahydrofuran, di-n-butyl ether and 1,4-dioxane, hydrocarbons such as n-hexane, n-heptane, benzene, toluene, xylene and cumene, and chlorinated solvents such as chloroform and dichloroethylene, alone or in admixture of any. The reaction temperature is preferably from 50xc2x0 C. to 200xc2x0 C. though it varies with other reaction conditions. Most preferably, reaction is effected at a temperature near the boiling point of the solvent while distilling off the alcohol (ROH) formed during the reaction. The reaction time is desirably determined by monitoring the reaction until the completion by gas chromatography (GC) or silica gel thin-layer chromatography (TLC) because higher yields are expectable. The reaction time is usually about 1 to about 20 hours. From the reaction mixture, the end cyclic acetal compound (i) is obtained by a conventional aqueous work-up step. If necessary, the end compound (i) is purified by any conventional technique such as distillation or chromatography. Alternatively, the end compound (i) is isolated by direct distillation of the reaction mixture.
As described above, glycerol formal contains a 5-membered ring acetal structure (iii) and an isomer of 6-membered ring acetal structure (iv), and the actual product obtained by the above methods is a mixture of a 5-membered ring acetal compound (i) and a 6-membered ring acetal compound (v). When this monomeric mixture is used for polymerization, the resulting polymer contains units based on the 5-membered ring acetal compound (i) and exhibits the same effects as a homopolymer obtained using the 5-membered ring acetal compound (i) alone.
It is noted that the proportion of 5-membered ring acetal compound (i) and 6-membered ring acetal compound (v) in the mixture is usually between 7:3 and 3:7 and especially between 6:4 and 4:6 in molar ratio although it varies with the mixed proportion of 5-membered ring acetal compound (iii) and 6-membered ring acetal compound (iv) in the glycerol formal.
According to the second aspect of the invention, a novel polymer is obtained using the cyclic acetal compound or cyclic acetal compound mixture described above. The polymer is defined as comprising recurring units of the following general formula (1-1) or (1-2) and having a weight average molecular weight of 1,000 to 500,000,
wherein R is hydrogen or methyl, k is 0 or 1, and n is an integer of 0 to 6.
In another embodiment, the polymer contains recurring units of the following general formula (1xe2x80x2-1) or (1xe2x80x2-2) in addition to the above units, especially in accordance with formula (1-1) or (1-2), respectively. 
Herein R is hydrogen or methyl, k is 0 or 1, and n is an integer from 0 to 6.
More specifically, the polymers of the invention are divided into the following six subgenuses of polymers.
Subgenus (1) includes polymers comprising recurring units of the following general formula (2-1) as well as the recurring units of formula (1-1). 
Herein k is as defined above, R1 is hydrogen, methyl or CH2CO2R3, R2 is hydrogen, methyl or CO2R3, R3 is a straight, branched or cyclic alkyl group of 1 to 15 carbon atoms, R4 is an acid labile group, R5 is selected from the class consisting of a halogen atom, a hydroxyl group, a straight, branched or cyclic alkoxy, acyloxy, alkoxycarbonyloxy or alkylsulfonyloxy group of 1 to 15 carbon atoms, and a straight, branched or cyclic alkoxyalkoxy group of 2 to 15 carbon atoms, in which some or all of the hydrogen atoms on constituent carbon atoms may be substituted with halogen atoms, Z is a single bond or a straight, branched or cyclic (h+2)-valent hydrocarbon group of 1 to 5 carbon atoms, in which at least one methylene may be substituted with oxygen to form a chain-like or cyclic ether or two hydrogen atoms on a common carbon may be substituted with oxygen to form a ketone, and h is 0, 1 or 2.
Subgenus (2) includes polymers comprising recurring units of the following general formulae (2-1) and (3) as well as the recurring units of formula (1-1). 
Herein k, h and R1 to R5 are as defined above.
Subgenus (3) includes polymers comprising recurring units of the following general formula (2-1) and/or recurring units of the following general formula (4), and recurring units of the following general formula (3) as well as the recurring units of formula (1-1). 
Herein k, h and R1 to R5 are as defined above.
Subgenus (4) includes polymers of subgenuses (1) to (3) further comprising recurring units of the general formula (1xe2x80x2-1).
Subgenus (5) includes polymers comprising recurring units of the following general formula (2-2) as well as the recurring units of formula (1-2). 
Herein k, h and R1 to R5 are as defined above.
Subgenus (6) includes polymers of subgenus (5) further comprising recurring units of the general formula (1xe2x80x2-2).
Herein, R1 is hydrogen, methyl or CH2CO2R3. R2 is hydrogen, methyl or CO2R3. R3 stands for straight, branched or cyclic alkyl groups of 1 to 15 carbon atoms, such as, for example, methyl, ethyl, n-propyl, isopropyl, n-butyl, sec-butyl, tert-butyl, tert-amyl, n-pentyl, n-hexyl, cyclopentyl, cyclohexyl, ethylcyclopentyl, butylcyclopentyl, ethylcyclohexyl, butylcyclohexyl, adamantyl, ethyladamantyl and butyladamantyl. R4 stands for acid labile groups to be described later.
R5 is selected from among a halogen atom, a hydroxyl group, a straight, branched or cyclic alkoxy, acyloxy, alkoxycarbonyloxy or alkylsulfonyloxy group of 1 to 15 carbon atoms, and a straight, branched or cyclic alkoxyalkoxy group of 2 to 15 carbon atoms, in which some or all of the hydrogen atoms on constituent carbon atoms may be substituted with halogen atoms. Exemplary of R5 are fluoro, chloro, bromo, methoxy, ethoxy, n-propoxy, isopropoxy, n-butoxy, sec-butoxy, tert-butoxy, tert-amyloxy, n-pentoxy, n-hexyloxy, cyclopentyloxy, cyclohexyloxy, ethylcyclopentyloxy, butylcyclopentyloxy, ethylcyclohexyloxy, butylcyclohexyloxy, adamantyloxy, ethyladamantyloxy, butyladamantyloxy, formyloxy, acetoxy, ethylcarbonyloxy, pivaloyloxy, methoxycarbonyloxy, ethoxycarbonyloxy, tert-butoxycarbonyloxy, methanesulfonyloxy, ethanesulfonyloxy, n-butanesulfonyloxy, trifluoroacetoxy, trichloroacetoxy, 2,2,2-trifluoroethylcarbonyloxy, methoxymethoxy, 1-ethoxyethoxy, 1-ethoxypropoxy, 1-tert-butoxyethoxy, 1-cyclohexyloxyethoxy, 2-tetrahydrofuranyloxy, and 2-tetrahydropyranyloxy.
Z is a single bond or a straight, branched or cyclic (h+2)-valent hydrocarbon group of 1 to 5 carbon atoms, in which at least one methylene may be substituted with oxygen to form a chain-like or cyclic ether or two hydrogen atoms on a common carbon may be substituted with oxygen to form a ketone. In case of h=0, for example, exemplary Z groups are methylene, ethylene, trimethylene, tetramethylene, pentamethylene, hexamethylene, 1,2-propanediyl, 1,3-butanediyl, 1-oxo-2-oxapropane-1,3-diyl, 3-methyl-1-oxo-2-oxabutane-1,4-diyl. In case of hxe2x89xa00, exemplary Z groups are (h+2)-valent groups obtained by eliminating one or two hydrogen atoms from the above-exemplified groups.
The acid labile groups represented by R4 may be selected from a variety of such groups. Examples of the acid labile group are groups of the following general formulae (L1) to (L4), tertiary alkyl groups of 4 to 20 carbon atoms, preferably 4 to 15 carbon atoms, trialkylsilyl groups in which each alkyl moiety has 1 to 6 carbon atoms, and oxoalkyl groups of 4 to 20 carbon atoms. 
In these formulae and throughout the specification, the broken line denotes a free valence bond. RL01 and RL02 are hydrogen or straight, branched or cyclic alkyl groups of 1 to 18 carbon atoms, preferably 1 to 10 carbon atoms. Exemplary alkyl groups include methyl, ethyl, n-propyl, isopropyl, n-butyl, sec-butyl, tert-butyl, cyclopentyl, cyclohexyl, 2-ethylhexyl, and n-octyl. RL03 is a monovalent hydrocarbon group of 1 to 18 carbon atoms, preferably 1 to 10 carbon atoms, which may contain a hetero atom such as oxygen, examples of which include unsubstituted straight, branched or cyclic alkyl groups and straight, branched or cyclic alkyl groups in which some hydrogen atoms are replaced by hydroxyl, alkoxy, oxo, amino, alkylamino or the like. Illustrative examples are the substituted alkyl groups shown below. 
A pair of RL01 and RL02, RL02 and RL03, or RL02 and RL03 may form a ring. Each of RL01, RL02 and RL03 is a straight or branched alkylene group of 1 to 18 carbon atoms, preferably 1 to 10 carbon atoms when they form a ring.
RL04 is a tertiary alkyl group of 4 to 20 carbon atoms, preferably 4 to 15 carbon atoms, a trialkylsilyl group in which each alkyl moiety has 1 to 6 carbon atoms, an oxoalkyl group of 4 to 20 carbon atoms, or a group of formula (L1). Exemplary tertiary alkyl groups are tert-butyl, tert-amyl, 1,1-diethylpropyl, 2-cyclopentylpropan-2-yl, 2-cyclohexylpropan-2-yl, 2-(bicyclo[2.2.1]heptan-2-yl)propan-2-yl, 2-(adamantan-1-yl)propan-2-yl, 1-ethylcyclopentyl, 1-butylcyclopentyl, 1-ethylcyclohexyl, 1-butylcyclohexyl, 1-ethyl-2-cyclopentenyl, 1-ethyl-2-cyclohexenyl, 2-methyl-2-adamantyl, and 2-ethyl-2-adamantyl. Exemplary trialkylsilyl groups are trimethylsilyl, triethylsilyl, and dimethyl-tert-butylsilyl. Exemplary oxoalkyl groups are 3-oxocyclohexyl, 4-methyl-2-oxooxan-4-yl, and 5-methyl-5-oxooxolan-4-yl. Letter y is an integer of 0 to 6.
RL05 is a monovalent hydrocarbon group of 1 to 8 carbon atoms which may contain a hetero atom or a substituted or unsubstituted aryl group of 6 to 20 carbon atoms. Examples of the monovalent hydrocarbon group which may contain a hetero atom include straight, branched or cyclic alkyl groups such as methyl, ethyl, n-propyl, isopropyl, n-butyl, sec-butyl, tert-butyl, tert-amyl, n-pentyl, n-hexyl, cyclopentyl, and cyclohexyl, and substituted groups in which some hydrogen atoms on the foregoing groups are substituted with hydroxyl, alkoxy, carboxy, alkoxycarbonyl, oxo, amino, alkylamino, cyano, mercapto, alkylthio, sulfo or other groups. Exemplary aryl groups are phenyl, methylphenyl, naphthyl, anthryl, phenanthryl, and pyrenyl. Letter m is equal to 0 or 1, n is equal to 0, 1, 2 or 3, and 2m+n is equal to 2 or 3.
RL06 is a monovalent hydrocarbon group of 1 to 8 carbon atoms which may contain a hetero atom or a substituted or unsubstituted aryl group of 6 to 20 carbon atoms. Examples of these groups are the same as exemplified for RL05.
RL07 to RL16 independently represent hydrogen or monovalent hydrocarbon groups of 1 to 15 carbon atoms which may contain a hetero atom. Exemplary hydrocarbon groups are straight, branched or cyclic alkyl groups such as methyl, ethyl, n-propyl, isopropyl, n-butyl, sec-butyl, tert-butyl, tert-amyl, n-pentyl, n-hexyl, n-octyl, n-nonyl, n-decyl, cyclopentyl, cyclohexyl, cyclopentylmethyl, cyclopentylethyl, cyclopentylbutyl, cyclohexylmethyl, cyclohexylethyl and cyclohexylbutyl, and substituted ones of these groups in which some hydrogen atoms are replaced by hydroxyl, alkoxy, carboxy, alkoxycarbonyl, oxo, amino, alkylamino, cyano, mercapto, alkylthio, sulfo or other groups. Alternatively, RL07 to RL16, taken together, form a ring (for example, a pair of RL07 and RL08, RL07 and RL09, RL08 and RL10, RL09 and RL10, RL11 and RL12, RL13 and RL14, or a similar pair form a ring). Each of RL07 to RL16 represents a divalent C1-C15 hydrocarbon group which may contain a hetero atom, when they form a ring, examples of which are the ones exemplified above for the monovalent hydrocarbon groups, with one hydrogen atom being eliminated. Two of RL07 to RL16 which are attached to adjoining carbon atoms (for example, a pair of RL07 and RL09, RL09 and RL15, RL13 and RL15, or a similar pair) may bond together directly to form a double bond.
Of the acid labile groups of formula (L1), the straight and branched ones are exemplified by the following groups. 
Of the acid labile groups of formula (L1), the cyclic ones are, for example, tetrahydrofuran-2-yl, 2-methyltetrahydrofuran-2-yl, tetrahydropyran-2-yl, and 2-methyltetrahydropyran-2-yl.
Examples of the acid labile groups of formula (L2) include tert-butoxycarbonyl, tert-butoxycarbonylmethyl, tert-amyloxycarbonyl, tert-amyloxycarbonylmethyl, 1,1-diethylpropyloxycarbonyl, 1,1-diethylpropyloxycarbonylmethyl, 1-ethylcyclopentyloxycarbonyl, 1-ethylcyclopentyloxy-carbonylmethyl, 1-ethyl-2-cyclopentenyloxycarbonyl, 1-ethyl-2-cyclopentenyloxycarbonylmethyl, 1-ethoxyethoxycarbonyl-methyl, 2-tetrahydropyranyloxycarbonylmethyl, and 2-tetra-hydrofuranyloxycarbonylmethyl groups.
Examples of the acid labile groups of formula (L3) include 1-methylcyclopentyl, 1-ethylcyclopentyl, 1-n-propylcyclopentyl, 1-isopropylcyclopentyl, 1-n-butylcyclopentyl, 1-sec-butylcyclopentyl, 1-methylcyclohexyl, 1-ethylcyclohexyl, 3-methyl-1-cyclopenten-3-yl, 3-ethyl-1-cyclopenten-3-yl, 3-methyl-1-cyclohexen-3-yl, and 3-ethyl-1-cyclohexen-3-yl groups.
The acid labile groups of formula (L4) are exemplified by the following groups. 
Examples of the tertiary alkyl groups of 4 to 20 carbon atoms, trialkylsilyl groups in which each alkyl moiety has 1 to 6 carbon atoms, and oxoalkyl groups of 4 to 20 carbon atoms are as exemplified for RL04.
Illustrative, non-limiting, examples of the recurring units of formula (1-1) are given below. 
Illustrative, non-limiting, examples of the recurring units of formula (1-2) are given below. 
Illustrative examples of the recurring units of formula (1xe2x80x2-1) or (1xe2x80x2-2) correspond to the examples of the recurring units of formula (1-1) or (1-2), provided that the group (A) is replaced by the group (B) below. 
Illustrative, non-limiting, examples of the recurring units of formula (2-1) are given below. 
Illustrative, non-limiting, examples of the recurring units of formula (2-2) are given below. 
Illustrative, non-limiting, examples of the recurring units of formula (4) are given below. 
If desired, the polymers of the invention may further contain recurring units of one or more types selected from units of the following general formulae (M1) to (M8-2). 
Herein, R001 is hydrogen, methyl or CH2CO2R003. R002 is hydrogen, methyl or CO2R003. R003 is a straight, branched or cyclic alkyl group of 1 to 15 carbon atoms. R004 is hydrogen or a monovalent hydrocarbon group of 1 to 15 carbon atoms having a carboxyl or hydroxyl group. At least one of R005 to R008 represents a monovalent hydrocarbon group of 1 to 15 carbon atoms having a carboxyl or hydroxyl group while the remaining R""s independently represent hydrogen or a straight, branched or cyclic alkyl group of 1 to 15 carbon atoms. Alternatively, R005 to R008, taken together, may form a ring, and in that event, at least one of R005 to R008 is a divalent hydrocarbon group of 1 to 15 carbon atoms having a carboxyl or hydroxyl group, while the remaining R""s are independently single bonds or straight, branched or cyclic alkylene groups of 1 to 15 carbon atoms. R009 is a monovalent hydrocarbon group of 3 to 15 carbon atoms containing a xe2x80x94CO2xe2x80x94 partial structure. At least one of R010 to R013 is a monovalent hydrocarbon group of 2 to 15 carbon atoms containing a xe2x80x94CO2xe2x80x94 partial structure, while the remaining R""s are independently hydrogen or straight, branched or cyclic alkyl groups of 1 to 15 carbon atoms. R010 to R013, taken together, may form a ring, and in that event, at least one of R010 to R013 is a divalent hydrocarbon group of 1 to 15 carbon atoms containing a xe2x80x94CO2xe2x80x94 partial structure, while the remaining R""s are independently single bonds or straight, branched or cyclic alkylene groups of 1 to 15 carbon atoms. R014 is a polycyclic hydrocarbon group having 7 to 15 carbon atoms or an alkyl group containing a polycyclic hydrocarbon group. R015 is an acid labile group. X is CH2 or an oxygen atom. Letter k is equal to 0 or 1.
More illustratively, R003 is a straight, branched or cyclic alkyl group of 1 to 15 carbon atoms, for example, methyl, ethyl, n-propyl, isopropyl, n-butyl, sec-butyl, tert-butyl, tert-amyl, n-pentyl, n-hexyl, cyclopentyl, cyclohexyl, ethylcyclopentyl, butylcyclopentyl, ethylcyclo-hexyl, butylcyclohexyl, adamantyl, ethyladamantyl, and butyladamantyl.
R004 is hydrogen or a monovalent hydrocarbon group of 1 to 15 carbon atoms having a carboxyl or hydroxyl group, for example, carboxyethyl, carboxybutyl, carboxycyclopentyl, carboxycyclohexyl, carboxynorbornyl, carboxyadamantyl, hydroxyethyl, hydroxybutyl, hydroxycyclopentyl, hydroxy-cyclohexyl, hydroxynorbornyl, and hydroxyadamantyl.
At least one of R005 to R008 represents a monovalent hydrocarbon group of 1 to 15 carbon atoms having a carboxyl or hydroxyl group while the remaining R""s independently represent hydrogen or a straight, branched or cyclic alkyl group of 1 to 15 carbon atoms. Examples of the carboxyl or hydroxyl-bearing monovalent hydrocarbon group of 1 to 15 carbon atoms include carboxy, carboxymethyl, carboxyethyl, carboxybutyl, hydroxymethyl, hydroxyethyl, hydroxybutyl, 2-carboxyethoxycarbonyl, 4-carboxybutoxycarbonyl, 2-hydroxyethoxycarbonyl, 4-hydroxybutoxycarbonyl, carboxycyclopentyloxycarbonyl, carboxycyclohexyloxycarbonyl, carboxynorbornyloxycarbonyl, carboxyadamantyloxycarbonyl, hydroxycyclopentyloxycarbonyl, hydroxycyclohexyloxycarbonyl, hydroxynorbornyloxycarbonyl, and hydroxyadamantyloxycarbonyl. Examples of the straight, branched or cyclic alkyl group of 1 to 15 carbon atoms are the same as exemplified for R003.
Alternatively, R005 to R008, taken together, may form a ring, and in that event, at least one of R005 to R008 is a divalent hydrocarbon group of 1 to 15 carbon atoms having a carboxyl or hydroxyl group, while the remaining R""s are independently single bonds or straight, branched or cyclic alkylene groups of 1 to 15 carbon atoms. Examples of the carboxyl or hydroxyl-bearing divalent hydrocarbon group of 1 to 15 carbon atoms include the groups exemplified as the carboxyl or hydroxyl-bearing monovalent hydrocarbon group, with one hydrogen atom eliminated therefrom. Examples of the straight, branched or cyclic alkylene groups of 1 to 15 carbon atoms include the groups exemplified for R003, with one hydrogen atom eliminated therefrom.
R009 is a monovalent hydrocarbon group of 3 to 15 carbon atoms containing a xe2x80x94CO2xe2x80x94 partial structure, for example, 2-oxooxolan-3-yl, 4,4-dimethyl-2-oxooxolan-3-yl, 4-methyl-2-oxooxan-4-yl, 2-oxo-1,3-dioxolan-4-ylmethyl, and 5-methyl-2-oxooxolan-5-yl.
At least one of R010 to R013 is a monovalent hydrocarbon group of 2 to 15 carbon atoms containing a xe2x80x94CO2xe2x80x94 partial structure, while the remaining R""s are independently hydrogen or straight, branched or cyclic alkyl groups of 1 to 15 carbon atoms. Examples of the monovalent hydrocarbon group of 2 to 15 carbon atoms containing a xe2x80x94CO2xe2x80x94 partial structure include 2-oxooxolan-3-yloxycarbonyl, 4,4-dimethyl-2-oxooxolan3-yloxycarbonyl, 4-methyl-2-oxooxan-4-yloxy-carbonyl, 2-oxo-1,3-dioxolan-4-ylmethyloxycarbonyl, and 5-methyl-2-oxooxolan-5-yloxycarbonyl. Examples of the straight, branched or cyclic alkyl groups of 1 to 15 carbon atoms are the same as exemplified for R003.
R010 to R013, taken together, may form a ring, and in that event, at least one of R010 to R013 is a divalent hydrocarbon group of 1 to 15 carbon atoms containing a xe2x80x94CO2xe2x80x94 partial structure, while the remaining R""s are independently single bonds or straight, branched or cyclic alkylene groups of 1 to 15 carbon atoms. Examples of the divalent hydrocarbon group of 1 to 15 carbon atoms containing a xe2x80x94CO2xe2x80x94 partial structure include 1-oxo-2-oxapropane-1,3-diyl, 1,3-dioxo-2-oxapropane-1,3-diyl, 1-oxo-2-oxabutane-1,4-diyl, and 1,3-dioxo-2-oxabutane-1,4-diyl, as well as the groups exemplified as the monovalent hydrocarbon group containing a xe2x80x94CO2xe2x80x94 partial structure, with one hydrogen atom eliminated therefrom. Examples of the straight, branched or cyclic alkylene groups of 1 to 15 carbon atoms include the groups exemplified for R003, with one hydrogen atom eliminated therefrom.
R014 is a polycyclic hydrocarbon group having 7 to 15 carbon atoms or an alkyl group containing a polycyclic hydrocarbon group, for example, norbornyl, bicyclo[3.3.1]-nonyl, tricyclo[5.2.1.02.6]decyl, adamantyl, ethyladamantyl, butyladamantyl, norbornylmethyl, and adamantylmethyl.
R015 is an acid labile group, examples of which are the same as described above. X is CH2 or an oxygen atom. Letter k is equal to 0 or 1.
The recurring units of formulae (M1) to (M8-2) are effective for imparting such desired properties as developer affinity, substrate adhesion and etching resistance to a resist composition based on a polymer comprising these recurring units. By adjusting the content of these recurring units, the performance of the resist composition can be finely adjusted.
The polymers of the invention have a weight average molecular weight of about 1,000 to 500,000, preferably about 3,000 to 100,000. Outside the range, the etching resistance may become extremely low and the resolution may become low because a substantial difference in rate of dissolution before and after exposure is lost.
The polymer of the invention can be prepared through copolymerization reaction using a compound of the following general formula (1a) or a mixture of a compound of formula (1a) and a compound of the following general formula (1axe2x80x2) as a first monomer, one, two or three members selected from compounds of the following general formulae (2a) to (4a) as second to fourth monomers, and optionally, one or more members selected from compounds of the following general formulae (M1a) to (M8a) as subsequent monomers. 
Herein, k, h, n, R, R1 to R5 are as defined above. 
Herein, k, R001 to R015, and X are as defined above.
By properly adjusting the proportion of the respective monomers used in the copolymerization reaction, the polymer can be tailored so that it may exert the preferred performance when blended in resist compositions.
In addition to (i) the monomer of formula (1a) or the mixture of monomers of formulae (1a) and (1axe2x80x2), (ii) the monomer or monomers of formulas (2a) to (4a), and (iii) the monomer or monomers of formulae (M1a) to (M8a), the polymer of the invention may have copolymerized therewith (iv) another monomer having a carbon-to-carbon double bond other than (i) to (iii). Examples of the additional monomer (iv) include substituted acrylic acid esters such as methyl methacrylate, methyl crotonate, dimethyl maleate, and dimethyl itaconate, unsaturated carboxylic acids such as maleic acid, fumaric acid and itaconic acid, substituted or unsubstituted norbornenes such as norbornene and methyl norbornene-5-carboxylate, and unsaturated acid anhydrides such as itaconic anhydride.
In the polymers of the invention, the preferred proportion of recurring units based on the respective monomers is in the following range, though not limited thereto.
(I) When the polymer is comprised of recurring units of formula (1-1) or formulae (1-1) and (1xe2x80x2-1) and recurring units of formula (2-1), it contains
(i) 1 to 90%, preferably 5 to 80%, and more preferably 10 to 70% of recurring units of formula (1-1) based on the monomer of formula (1a) or recurring units of formulae (1-1) and (1xe2x80x2-1),
(ii) 1 to 90%, preferably 5 to 80%, and more preferably 10 to 70% of recurring units of formula (2-1) based on the monomer of formula (2a),
(iii) 0 to 50%, preferably 0 to 40%, and more preferably 0 to 30% of recurring units of formula (M5-1) to (M8-1) based on the monomers of formula (M5a) to (M8a), and
(iv) 0 to 50%, preferably 0 to 40%, and more preferably 0 to 30% of recurring units based on another monomer.
(II) When the polymer is comprised of recurring units of formula (1-1) or formulae (1-1) and (1xe2x80x2-1), recurring units of formula (2-1) and recurring units of formula (3), it contains
(i) 1 to 49%, preferably 3 to 45%, and more preferably 5 to 40% of recurring units of formula (1-1) based on the monomer of formula (1a) or recurring units of formulae (1-1) and (1xe2x80x2-1),
(ii) 1 to 49%, preferably 3 to 45%, and more preferably 5 to 40% of recurring units of formula (2-1) based on the monomer of formula (2a),
(iii) 50 mol % of recurring units of formula (3) based on the monomer of formula (3a),
(iv) 0 to 25%, preferably 0 to 20%, and more preferably 0 to 15% of recurring units of formula (M5-1) to (M8-1) based on the monomers of formula (M5a) to (M8a), and
(v) 0 to 25%, preferably 0 to 20%, and more preferably 0 to 15% of recurring units based on another monomer.
(III) When the polymer is comprised of recurring units of formula (1-1) or formulae (1-1) and (1xe2x80x2-1), recurring units of formula (2-1) and/or recurring units of formula (4), and recurring units of formula (3), it contains
(i) 1 to 49%, preferably 3 to 45%, and more preferably 5 to 40% of recurring units of formula (1-1) based on the monomer of formula (1a) or recurring units of formulae (1-1) and (1-1),
(ii) 0 to 40%, preferably 0 to 35%, and more preferably 0 to 30% of recurring units of formula (2-1) based on the monomer of formula (2a),
(iii) 1 to 80%, preferably 1 to 70%, and more preferably 1 to 50% of recurring units of formula (4) based on the monomer of formula (4a),
(iv) 1 to 49%, preferably 5 to 45%, and more preferably 10 to 40% of recurring units of formula (3) based on the monomer of formula (3a),
(v) 0 to 25%, preferably 0 to 20%, and more preferably 0 to 15% of recurring units of formula (M1) to (M8-1) based on the monomers of formula (M1a) to (M8a), and
(vi) 0 to 25%, preferably 0 to 20%, and more preferably 0 to 15% of recurring units based on another monomer.
(IV) When the polymer is comprised of recurring units of formula (1-2) or formulae (1-2) and (1xe2x80x2-2) and recurring units of formula (2-2), it contains
(i) 1 to 90%, preferably 5 to 80%, and more preferably 10 to 70% of recurring units of formula (1-2) based on the monomer of formula (1a) or recurring units of formulae (1-2) and (1xe2x80x2-2),
(ii) 1 to 90%, preferably 5 to 80%, and more preferably 10 to 70% of recurring units of formula (2-2) based on the monomer of formula (2a),
(iii) 0 to 50%, preferably 0 to 40%, and more preferably 0 to 30% of recurring units of formula (M5-2) to (M8-2) based on the monomers of formula (M5a) to (M8a), and
(iv) 0 to 50%, preferably 0 to 40%, and more preferably 0 to 30% of recurring units based on another monomer.
It is noted that where a polymer contains recurring units of formula (1-1) and recurring units of formula (1xe2x80x2-1), their proportion is preferably between 7:3 and 3:7, and especially between 6:4 and 4:6 in molar ratio, though not limited thereto. Also where a polymer contains recurring units of formula (1-2) and recurring units of formula (1xe2x80x2-2), their proportion is preferably between 7:3 and 3:7, and especially between 6:4 and 4:6 in molar ratio.
A variety of copolymerization reaction methods may be used for the preparation of the polymer according to the invention. The preferred polymerization reaction is radical polymerization, anionic polymerization or coordination polymerization.
For radical polymerization, preferred reaction conditions include (a) a solvent selected from among hydrocarbons such as benzene, ethers such as tetrahydrofuran, alcohols such as ethanol, and ketones such as methyl isobutyl ketone, (b) a polymerization initiator selected from azo compounds such as 2,2xe2x80x2-azobisisobutyronitrile and peroxides such as benzoyl peroxide and lauroyl peroxide, (c) a temperature of about 0xc2x0 C. to about 100xc2x0 C., and (d) a time of about xc2xd hour to about 48 hours. Reaction conditions outside the described range may be employed if desired.
For anionic polymerization, preferred reaction conditions include (a) a solvent selected from among hydrocarbons such as benzene, ethers such as tetrahydrofuran, and liquid ammonia, (b) a polymerization initiator selected from metals such as sodium and potassium, alkyl metals such as n-butyllithium and sec-butyllithium, ketyl, and Grignard reagents, (c) a temperature of about xe2x88x9278xc2x0 C. to about 0xc2x0 C., (d) a time of about xc2xd hour to about 48 hours, and (e) a stopper selected from among proton-donative compounds such as methanol, halides such as methyl iodide, and electrophilic compounds. Reaction conditions outside the described range may be employed if desired.
For coordination polymerization, preferred reaction conditions include (a) a solvent selected from among hydrocarbons such as n-heptane and toluene, (b) a catalyst selected from Ziegler-Natta catalysts comprising a transition metal (e.g., titanium) and alkylaluminum, Phillips catalysts of metal oxides having chromium or nickel compounds carried thereon, and olefin-metathesis mixed catalysts as typified by tungsten and rhenium mixed catalysts, (c) a temperature of about 0xc2x0 C. to about 100xc2x0 C., and (d) a time of about xc2xd hour to about 48 hours. Reaction conditions outside the described range may be employed if desired.
Since the polymer of the invention is useful as the base polymer of a resist composition, the third aspect of the invention provides a resist composition, especially chemically amplified resist composition, comprising the polymer. Preferably, the resist composition is defined as comprising the polymer, a photoacid generator, and an organic solvent.
The photoacid generator is a compound capable of generating an acid upon exposure to high energy radiation or electron beams and includes the following:
(i) onium salts of the formula (P1a-1), (P1a-2) or (P1b),
(ii) diazomethane derivatives of the formula (P2),
(iii) glyoxime derivatives of the formula (P3),
(iv) bissulfone derivatives of the formula (P4),
(v) sulfonic acid esters of N-hydroxyimide compounds of the formula (P5),
(vi) xcex2-ketosulfonic acid derivatives,
(vii) disulfone derivatives,
(viii) nitrobenzylsulfonate derivatives, and
(ix) sulfonate derivatives.
These photoacid generators are described in detail.
(i) Onium Salts of Formula (P1a-1), (P1a-2) or (P1b) 
Herein, R101a, R101b, and R101c independently represent straight, branched or cyclic alkyl, alkenyl, oxoalkyl or oxoalkenyl groups of 1 to 12 carbon atoms, aryl groups of 6 to 20 carbon atoms, or aralkyl or aryloxoalkyl groups of 7 to 12 carbon atoms, wherein some or all of the hydrogen atoms may be replaced by alkoxy or other groups. Also, R101b and R101c, taken together, may form a ring. R101b and R101c each are alkylene groups of 1 to 6 carbon atoms when they form a ring. Kxe2x88x92 is a non-nucleophilic counter ion.
R101a, R101b, and R101c may be the same or different and are illustrated below. Exemplary alkyl groups include methyl, ethyl, propyl, isopropyl, n-butyl, sec-butyl, tert-butyl, pentyl, hexyl, heptyl, octyl, cyclopentyl, cyclohexyl, cycloheptyl, cyclopropylmethyl, 4-methylcyclohexyl, cyclohexylmethyl, norbornyl, and adamantyl. Exemplary alkenyl groups include vinyl, allyl, propenyl, butenyl, hexenyl, and cyclohexenyl. Exemplary oxoalkyl groups include 2-oxocyclopentyl and 2-oxocyclohexyl as well as 2-oxopropyl, 2-cyclopentyl-2-oxoethyl, 2-cyclohexyl-2-oxoethyl, and 2-(4-methylcyclohexyl)-2-oxoethyl. Exemplary aryl groups include phenyl and naphthyl; alkoxyphenyl groups such as p-methoxyphenyl, m-methoxyphenyl, o-methoxyphenyl, ethoxyphenyl, p-tert-butoxyphenyl, and m-tert-butoxyphenyl; alkylphenyl groups such as 2-methylphenyl, 3-methylphenyl, 4-methylphenyl, ethylphenyl, 4-tert-butylphenyl, 4-butylphenyl, and dimethylphenyl; alkylnaphthyl groups such as methylnaphthyl and ethylnaphthyl; alkoxynaphthyl groups such as methoxynaphthyl and ethoxynaphthyl; dialkylnaphthyl groups such as dimethylnaphthyl and diethylnaphthyl; and dialkoxynaphthyl groups such as dimethoxynaphthyl and diethoxynaphthyl. Exemplary aralkyl groups include benzyl, phenylethyl, and phenethyl. Exemplary aryloxoalkyl groups are 2-aryl-2-oxoethyl groups such as 2-phenyl-2-oxoethyl, 2-(1-naphthyl)-2-oxoethyl, and 2-(2-naphthyl)-2-oxoethyl. Examples of the non-nucleophilic counter ion represented by Kxe2x88x92 include halide ions such as chloride and bromide ions, fluoroalkylsulfonate ions such as triflate, 1,1,1-trifluoroethanesulfonate, and nonafluorobutanesulfonate, arylsulfonate ions such as tosylate, benzenesulfonate, 4-fluorobenzenesulfonate, and 1,2,3,4,5-pentafluorobenzenesulfonate, and alkylsulfonate ions such as mesylate and butanesulfonate. 
Herein, R101a and R102b independently represent straight, branched or cyclic alkyl groups of 1 to 8 carbon atoms. R103 represents a straight, branched or cyclic alkylene groups of 1 to 10 carbon atoms. R104a and R104b independently represent 2-oxoalkyl groups of 3 to 7 carbon atoms. Kxe2x88x92 is a non-nucleophilic counter ion.
Illustrative of the groups represented by R102a and R102b are methyl, ethyl, propyl, isopropyl, n-butyl, sec-butyl, tert-butyl, pentyl, hexyl, heptyl, octyl, cyclopentyl, cyclohexyl, cyclopropylmethyl, 4-methylcyclohexyl, and cyclohexylmethyl. Illustrative of the groups represented by R103 are methylene, ethylene, propylene, butylene, pentylene, hexylene, heptylene, octylene, nonylene, 1,4-cyclohexylene, 1,2-cyclohexylene, 1,3-cyclopentylene, 1,4-cyclooctylene, and 1,4-cyclohexanedimethylene. Illustrative of the groups represented by R104a and R104b are 2-oxopropyl, 2-oxocyclopentyl, 2-oxocyclohexyl, and 2-oxocycloheptyl. Illustrative examples of the counter ion represented by Kxe2x88x92 are the same as exemplified for formulae (P1a-1) and (P1a-2).
(ii) Diazomethane Derivatives of Formula (P2) 
Herein, R105 and R106 independently represent straight, branched or cyclic alkyl or halogenated alkyl groups of 1 to 12 carbon atoms, aryl or halogenated aryl groups of 6 to 20 carbon atoms, or aralkyl groups of 7 to 12 carbon atoms.
Of the groups represented by R105 and R106, exemplary alkyl groups include methyl, ethyl, propyl, isopropyl, n-butyl, sec-butyl, tert-butyl, pentyl, hexyl, heptyl, octyl, amyl, cyclopentyl, cyclohexyl, cycloheptyl, norbornyl, and adamantyl. Exemplary halogenated alkyl groups include trifluoromethyl, 1,1,1-trifluoroethyl, 1,1,1-trichloroethyl, and nonafluorobutyl. Exemplary aryl groups include phenyl; alkoxyphenyl groups such as p-methoxyphenyl, m-methoxyphenyl, o-methoxyphenyl, ethoxyphenyl, p-tert-butoxyphenyl, and m-tert-butoxyphenyl; and alkylphenyl groups such as 2-methylphenyl, 3-methylphenyl, 4-methylphenyl, ethylphenyl, 4-tert-butylphenyl, 4-butylphenyl, and dimethylphenyl. Exemplary halogenated aryl groups include fluorophenyl, chlorophenyl, and 1,2,3,4,5-pentafluorophenyl. Exemplary aralkyl groups include benzyl and phenethyl.
(iii) Glyoxime Derivatives of Formula (P3) 
Herein, R107, R108, and R109 independently represent straight, branched or cyclic alkyl or halogenated alkyl groups of 1 to 12 carbon atoms, aryl or halogenated aryl groups of 6 to 20 carbon atoms, or aralkyl groups of 7 to 12 carbon atoms. Also, R108 and R109, taken together, may form a ring. R108 and R109 each are straight or branched alkylene groups of 1 to 6 carbon atoms when they form a ring.
Illustrative examples of the alkyl, halogenated alkyl, aryl, halogenated aryl, and aralkyl groups represented by R107, R108, and R109 are the same as exemplified for R105 and R106. Examples of the alkylene groups represented by R108 and R109 include methylene, ethylene, propylene, butylene, and hexylene.
(iv) Bissulfone Derivatives of Formula (P4) 
Herein, R101a and R101b are as defined above. (v) Sulfonic acid esters of N-hydroxyimide compounds of formula (P5) 
Herein, R110 is an arylene group of 6 to 10 carbon atoms, alkylene group of 1 to 6 carbon atoms, or alkenylene group of 2 to 6 carbon atoms wherein some or all of the hydrogen atoms may be replaced by straight or branched alkyl or alkoxy groups of 1 to 4 carbon atoms, nitro, acetyl, or phenyl groups. R111 is a straight, branched or cyclic alkyl group of 1 to 8 carbon atoms, alkenyl, alkoxyalkyl, phenyl or naphthyl group wherein some or all of the hydrogen atoms may be replaced by alkyl or alkoxy groups of 1 to 4 carbon atoms, phenyl groups (which may have substituted thereon an alkyl or alkoxy of 1 to 4 carbon atoms, nitro, or acetyl group), hetero-aromatic groups of 3 to 5 carbon atoms, or chlorine or fluorine atoms.
Of the groups represented by R110, exemplary arylene groups include 1,2-phenylene and 1,8-naphthylene; exemplary alkylene groups include methylene, 1,2-ethylene, 1,3-propylene, 1,4-butylene, 1-phenyl-1,2-ethylene, and norbornane-2,3-diyl; and exemplary alkenylene groups include 1,2-vinylene, 1-phenyl-1,2-vinylene, and 5-norbornene-2,3-diyl. Of the groups represented by R111, exemplary alkyl groups are as exemplified for R101a to R101c; exemplary alkenyl groups include vinyl, 1-propenyl, allyl, 1-butenyl, 3-butenyl, isoprenyl, 1-pentenyl, 3-pentenyl, 4-pentenyl, dimethylallyl, 1-hexenyl, 3-hexenyl, 5-hexenyl, 1-heptenyl, 3-heptenyl, 6-heptenyl, and 7-octenyl; and exemplary alkoxyalkyl groups include methoxymethyl, ethoxymethyl, propoxymethyl, butoxymethyl, pentyloxymethyl, hexyloxymethyl, heptyloxymethyl, methoxyethyl, ethoxyethyl, propoxyethyl, butoxyethyl, pentyloxyethyl, hexyloxyethyl, methoxypropyl, ethoxypropyl, propoxypropyl, butoxypropyl, methoxybutyl, ethoxybutyl, propoxybutyl, methoxypentyl, ethoxypentyl, methoxyhexyl, and methoxyheptyl.
Of the substituents on these groups, the alkyl groups of 1 to 4 carbon atoms include methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl and tert-butyl; the alkoxy groups of 1 to 4 carbon atoms include methoxy, ethoxy, propoxy, isopropoxy, n-butoxy, isobutoxy, and tert-butoxy; the phenyl groups which may have substituted thereon an alkyl or alkoxy of 1 to 4 carbon atoms, nitro, or acetyl group include phenyl, tolyl, p-tert-butoxyphenyl, p-acetylphenyl and p-nitrophenyl; the hetero-aromatic groups of 3 to 5 carbon atoms include pyridyl and furyl.
Illustrative examples of the photoacid generator include:
onium salts such as diphenyliodonium trifluoromethanesulfonate, (p-tert-butoxyphenyl)phenyliodonium trifluoro-methanesulfonate, diphenyliodonium p-toluenesulfonate, (p-tert-butoxyphenyl)phenyliodonium p-toluenesulfonate, triphenylsulfonium trifluoromethanesulfonate, (p-tert-butoxyphenyl)diphenylsulfonium trifluoromethanesulfonate, bis(p-tert-butoxyphenyl)phenylsulfonium trifluoromethanesulfonate, tris(p-tert-butoxyphenyl)sulfonium trifluoro-methanesulfonate, triphenylsulfonium p-toluenesulfonate, (p-tert-butoxyphenyl)diphenylsulfonium p-toluenesulfonate, bis(p-tert-butoxyphenyl)phenylsulfonium p-toluenesulfonate, tris(p-tert-butoxyphenyl)sulfonium p-toluenesulfonate, triphenylsulfonium nonafluorobutanesulfonate, triphenylsulfonium butanesulfonate, trimethylsulfonium trifluoromethanesulfonate, trimethylsulfonium p-toluenesulfonate, cyclohexylmethyl(2-oxocyclohexyl)sulfonium trifluoromethanesulfonate, cyclohexylmethyl(2-oxocyclohexyl)sulfonium p-toluenesulfonate, dimethylphenylsulfonium trifluoromethanesulfonate, dimethylphenylsulfonium p-toluenesulfonate, dicyclohexylphenylsulfonium trifluoromethanesulfonate, dicyclohexylphenylsulfonium p-toluenesulfonate, trinaphthylsulfonium trifluoromethanesulfonate, cyclohexylmethyl(2-oxocyclohexyl)sulfonium trifluoromethanesulfonate, (2-norbornyl)methyl(2-oxocyclohexyl)sulfonium trifluoromethanesulfonate, ethylenebis[methyl(2-oxocyclopentyl)sulfonium trifluoromethanesulfonate], and 1,2xe2x80x2-naphthylcarbonylmethyltetrahydrothiophenium triflate;
diazomethane derivatives such as bis(benzenesulfonyl)-diazomethane, bis(p-toluenesulfonyl)diazomethane, bis-(xylenesulfonyl)diazomethane, bis(cyclohexylsulfonyl)diazo-methane, bis(cyclopentylsulfonyl)diazomethane, bis(n-butylsulfonyl)diazomethane, bis(isobutylsulfonyl)diazoethane, bis(sec-butylsulfonyl)diazomethane, bis(n-propylsulfonyl)-diazomethane, bis(isopropylsulfonyl)diazomethane, bis(tert-butylsulfonyl)diazomethane, bis(n-amylsulfonyl)diazomethane, bis(isoamylsulfonyl)diazomethane, bis(sec-amylsulfonyl)diazomethane, bis(tert-amylsulfonyl)diazomethane, 1-cyclohexylsulfonyl-1-(tert-butylsulfonyl)diazomethane, 1-cyclohexylsulfonyl-1-(tert-amylsulfonyl)diazomethane, and 1-tertamylsulfonyl-1-(tert-butylsulfonyl)diazomethane;
glyoxime derivatives such as bis-O-(p-toluenesulfonyl)-xcex1-dimethylglyoxime, bis-O-(p-toluenesulfonyl)-xcex1-diphenylglyoxime, bis-O-(p-toluenesulfonyl)-xcex1-dicyclohexylglyoxime, bis-O-(p-toluenesulfonyl)-2,3-pentanedioneglyoxime, bis-O-(p-toluenesulfonyl)-2-methyl-3,4-pentanedioneglyoxime, bis-O-(n-butanesulfonyl)-xcex1-dimethylglyoxime, bis-O-(n-butanesulfonyl)-xcex1-diphenylglyoxime, bis-O-(n-butanesulfonyl)-xcex1-dicyclohexylglyoxime, bis-O-(n-butanesulfonyl)-2,3-pentanedioneglyoxime, bis-O-(n-butanesulfonyl)-2-methyl-3,4-pentanedioneglyoxime, bis-O-(methanesulfonyl)-xcex1-dimethylglyoxime, bis-O-(trifluoromethanesulfonyl)-xcex1-dimethylglyoxime, bis-O-(1,1,1-trifluoroethanesulfonyl)-xcex1-dimethylglyoxime, bis-O-(tert-butanesulfonyl)-xcex1-dimethyl-glyoxime, bis-O-(perfluorooctanesulfonyl)-xcex1-dimethylglyoxime, bis-O-(cyclohexanesulfonyl)-xcex1-dimethylglyoxime, bis-O-(benzenesulfonyl)-xcex1-dimethylglyoxime, bis-O-(p-fluoro-benzenesulfonyl)-xcex1-dimethylglyoxime, bis-O-(p-tert-butyl-benzenesulfonyl)-xcex1-dimethylglyoxime, bis-O-(xylenesulfonyl)-xcex1-dimethylglyoxime, and bis-O-(camphorsulfonyl)-xcex1-dimethylglyoxime;
bissulfone derivatives such as bisnaphthylsulfonylmethane, bistrifluoromethylsulfonylmethane, bismethylsulfonylmethane, bisethylsulfonylmethane, bispropylsulfonylmethane, bisisopropylsulfonylmethane, bis-p-toluenesulfonylmethane, and bisbenzenesulfonylmethane;
xcex2-ketosulfone derivatives such as 2-cyclohexylcarbonyl-2-(p-toluenesulfonyl)propane and 2-isopropylcarbonyl-2-(p-toluenesulfonyl)propane;
disulfone derivatives such as diphenyl disulfone and dicyclohexyl disulfone;
nitrobenzyl sulfonate derivatives such as 2,6-dinitrobenzyl p-toluenesulfonate and 2,4-dinitrobenzyl p-toluenesulfonate;
sulfonic acid ester derivatives such as 1,2,3-tris-(methanesulfonyloxy)benzene, 1,2,3-tris(trifluoromethanesulfonyloxy)benzene, and 1,2,3-tris(p-toluenesulfonyloxy)-benzene; and
sulfonic acid esters of N-hydroxyimides such as N-hydroxysuccinimide methanesulfonate, N-hydroxysuccinimide trifluoromethanesulfonate, N-hydroxysuccinimide ethanesulfonate, N-hydroxysuccinimide 1-propanesulfonate, N-hydroxysuccinimide 2-propanesulfonate, N-hydroxysuccinimide 1-pentanesulfonate, N-hydroxysuccinimide 1-octanesulfonate, N-hydroxysuccinimide p-toluenesulfonate, N-hydroxysuccinimide p-methoxybenzenesulfonate, N-hydroxysuccinimide 2-chloroethanesulfonate, N-hydroxysuccinimide benzenesulfonate, N-hydroxysuccinimide 2,4,6-trimethylbenzenesulfonate, N-hydroxysuccinimide 1-naphthalenesulfonate, N-hydroxysuccinimide 2-naphthalenesulfonate, N-hydroxy-2-phenylsuccinimide methanesulfonate, N-hydroxymaleimide methanesulfonate, N-hydroxymaleimide ethanesulfonate, N-hydroxy-2-phenylmaleimide methanesulfonate, N-hydroxyglutarimide methanesulfonate, N-hydroxyglutarimide benzenesulfonate, N-hydroxyphthalimide methanesulfonate, N-hydroxyphthalimide benzenesulfonate, N-hydroxyphthalimide trifluoromethanesulfonate, N-hydroxyphthalimide p-toluenesulfonate, N-hydroxynaphthalimide methanesulfonate, N-hydroxynaphthalimide benzenesulfonate, N-hydroxy-5-norbornene-2,3-dicarboxyimide methanesulfonate, N-hydroxy-5-norbornene-2,3-dicarboxyimide trifluoromethanesulfonate, and N-hydroxy-5-norbornene-2,3-dicarboxyimide p-toluenesulfonate.
Preferred among these photoacid generators are onium salts such as triphenylsulfonium trifluoromethanesulfonate, (p-tert-butoxyphenyl)diphenylsulfonium trifluoromethanesulfonate, tris(p-tert-butoxyphenyl)sulfonium trifluoromethanesulfonate, triphenylsulfonium p-toluenesulfonate, (p-tert-butoxyphenyl)diphenylsulfonium p-toluenesulfonate, tris(p-tert-butoxyphenyl)sulfonium p-toluenesulfonate, trinaphthylsulfonium trifluoromethanesulfonate, cyclohexylmethyl(2-oxocyclohexyl)sulfonium trifluoromethanesulfonate, (2-norbornyl)methyl(2-oxocylohexyl)sulfonium trifluoro methanesulfonate, and 1,2xe2x80x2-naphthylcarbonylmethyltetrahydrothiophenium triflate; diazomethane derivatives such as bis(benzenesulfonyl)diazomethane, bis(p-toluenesulfonyl)-diazomethane, bis(cyclohexylsulfonyl)diazomethane, bis(n-butylsulfonyl)diazomethane, bis(isobutylsulfonyl)diazo-methane, bis(sec-butylsulfonyl)diazomethane, bis(n-propylsulfonyl)diazomethane, bis(isopropylsulfonyl)diazomethane, and bis(tert-butylsulfonyl)diazomethane; glyoxime derivatives such as bis-O-(p-toluenesulfonyl)-xcex1-dimethylglyoxime and bis-O-(n-butanesulfonyl)-xcex1-dimethylglyoxime; bissulfone derivatives such as bisnaphthylsulfonylmethane; and sulfonic acid esters of N-hydroxyimide compounds such as N-hydroxysuccinimide methanesulfonate, N-hydroxysuccinimide trifluoromethanesulfonate, N-hydroxysuccinimide 1-propanesulfonate, N-hydroxysuccinimide 2-propanesulfonate, N-hydroxysuccinimide 1-pentanesulfonate, N-hydroxysuccinimide p-toluenesulfonate, N-hydroxynaphthalimide methanesulfonate, and N-hydroxynaphthalimide benzenesulfonate.
These photoacid generators may be used singly or in combinations of two or more thereof. Onium salts are effective for improving rectangularity, while diazomethane derivatives and glyoxime derivatives are effective for reducing standing waves. The combination of an onium salt with a diazomethane or a glyoxime derivative allows for fine adjustment of the profile.
The photoacid generator is added in an amount of 0.1 to 15 parts, and especially 0.5 to 8 parts by weight, per 100 parts by weight of the base resin (all parts are by weight, hereinafter). Less than 0.1 part of the photoacid generator would provide a poor sensitivity whereas more than parts of the photoacid generator would adversely affect transparency and resolution.
The organic solvent used herein may be any organic solvent in which the base resin, photoacid generator, and other components are soluble. Illustrative, non-limiting, examples of the organic solvent include ketones such as cyclohexanone and methyl-2-n-amylketone; alcohols such as 3-methoxybutanol, 3-methyl-3-methoxybutanol, 1-methoxy-2-propanol, and 1-ethoxy-2-propanol; ethers such as propylene glycol monomethyl ether, ethylene glycol monomethyl ether, propylene glycol monoethyl ether, ethylene glycol monoethyl ether, propylene glycol dimethyl ether, and diethylene glycol dimethyl ether; and esters such as propylene glycol monomethyl ether acetate, propylene glycol monoethyl ether acetate, ethyl lactate, ethyl pyruvate, butyl acetate, methyl 3-methoxypropionate, ethyl 3-ethoxypropionate, tert-butyl acetate, tert-butyl propionate, and propylene glycol mono-tert-butyl ether acetate. These solvents may be used alone or in combinations of two or more thereof. Of the above organic solvents, it is recommended to use diethylene glycol dimethyl ether and 1-ethoxy-2-propanol because the photoacid generator is most soluble therein, propylene glycol monomethyl ether acetate because it is a safe solvent, or a mixture thereof.
An appropriate amount of the organic solvent used is about 200 to 1,000 parts, especially about 400 to 800 parts by weight per 100 parts by weight of the base resin.
To the resist composition of the invention, another polymer other than the inventive polymer comprising recurring units of formula (1-1) or (1-2) may also be added. The other polymers that can be added to the resist composition are, for example, those polymers comprising units of the following formula (R1) and/or (R2) and having a weight average molecular weight of about 1,000 to about 500,000, especially about 5,000 to about 100,000 although the other polymers are not limited thereto. 
Herein, R001 is hydrogen, methyl or CH2CO2R003. R002 is hydrogen, methyl or CO2R003. R003 is a straight, branched or cyclic alkyl group of 1 to 15 carbon atoms. R004 is hydrogen or a monovalent hydrocarbon group of 1 to 15 carbon atoms having a carboxyl or hydroxyl group. At least one of R005 to R008 represents a monovalent hydrocarbon group of 1 to 15 carbon atoms having a carboxyl or hydroxyl group while the remaining R""s independently represent hydrogen or a straight, branched or cyclic alkyl group of 1 to 15 carbon atoms. Alternatively, R005 to R008, taken together, may form a ring, and in that event, at least one of R005 to R008 is a divalent hydrocarbon group of 1 to 15 carbon atoms having a carboxyl or hydroxyl group, while the remaining R""s are independently single bonds or straight, branched or cyclic alkylene groups of 1 to 15 carbon atoms. R009 is a monovalent hydrocarbon group of 3 to 15 carbon atoms containing a xe2x80x94CO2xe2x80x94 partial structure. At least one of R010 to R013 is a monovalent hydrocarbon group of 2 to 15 carbon atoms containing a xe2x80x94CO2xe2x80x94 partial structure, while the remaining R""s are independently hydrogen or straight, branched or cyclic alkyl groups of 1 to 15 carbon atoms. R010 to R013, taken together, may form a ring, and in that event, at least one of R010 to R013 is a divalent hydrocarbon group of 1 to 15 carbon atoms containing a xe2x80x94CO2xe2x80x94 partial structure, while the remaining R""s are independently single bonds or straight, branched or cyclic alkylene groups of 1 to 15 carbon atoms. R014 is a polycyclic hydrocarbon group having 7 to 15 carbon atoms or an alkyl group containing a polycyclic hydrocarbon group. R015 is an acid labile group. R016 is hydrogen or methyl. R017 is a straight, branched or cyclic alkyl group of 1 to 8 carbon atoms. X is CH2 or an oxygen atom. Letter kxe2x80x2 is equal to 0 or 1; a1xe2x80x2, a2xe2x80x2, a3xe2x80x2, b1xe2x80x2, b2xe2x80x2, b3xe2x80x2, c1xe2x80x2, c2xe2x80x2, c3xe2x80x2, d1xe2x80x2, d2xe2x80x2, d3xe2x80x2, and exe2x80x2 are numbers from 0 to less than 1, satisfying a1xe2x80x2+a2xe2x80x2+a3xe2x80x2+b1xe2x80x2+b2xe2x80x2+b3xe2x80x2+c1xe2x80x2+c2xe2x80x2+c3xe2x80x2+d1xe2x80x2+d2xe2x80x2+d3xe2x80x2+exe2x80x2=1; fxe2x80x2, gxe2x80x2, hxe2x80x2, ixe2x80x2, and jxe2x80x2 are numbers from 0 to less than 1, satisfying fxe2x80x2+gxe2x80x2+hxe2x80x2+ixe2x80x2+jxe2x80x2=1.
Exemplary groups of these R""s are as exemplified above.
The inventive polymer (comprising recurring units of formula (1-1) or (1-2)) and the other polymer are preferably blended in a weight ratio from 100:0 to 10:90, more preferably from 100:0 to 20:80. If the blend ratio of the inventive polymer is below this range, the resist composition would become poor in some of the desired properties. The properties of the resist composition can be adjusted by properly changing the blend ratio of the inventive polymer.
The other polymer is not limited to one type and a mixture of two or more other polymers may be added. The use of plural polymers allows for easy adjustment of resist properties.
To the resist composition, a dissolution regulator may be added. The dissolution regulator is a compound having on the molecule at least two phenolic hydroxyl groups, in which an average of from 0 to 100 molt of all the hydrogen atoms on the phenolic hydroxyl groups are replaced with acid labile groups or a compound having on the molecule at least one carboxyl group, in which an average of 50 to 100 molt of all the hydrogen atoms on the carboxyl groups are replaced with acid labile groups, both the compounds having an average molecular weight within a range of 100 to 1,000, and preferably 150 to 800.
The degree of substitution of the hydrogen atoms on the phenolic hydroxyl groups with acid labile groups is on average at least 0 mol %, and preferably at least 30 mol %, of all the phenolic hydroxyl groups. The upper limit is 100 mol %, and preferably 80 mol %. The degree of substitution of the hydrogen atoms on the carboxyl groups with acid labile groups is on average at least 50 mol %, and preferably at least 70 mol %, of all the carboxyl groups, with the upper limit being 100 mol %.
Preferable examples of such compounds having two or more phenolic hydroxyl groups or compounds having at least one carboxyl group include those of formulas (D1) to (D14) below. 
In these formulas, R201 and R202 are each hydrogen or a straight or branched alkyl or alkenyl of 1 to 8 carbon atoms; R203 is hydrogen, a straight or branched alkyl or alkenyl of 1 to 8 carbon atoms, or xe2x80x94(R207)hxe2x80x94COOH; R204 is xe2x80x94(CH2)ixe2x80x94 (where i=2 to 10), an arylene of 6 to 10 carbon atoms, carbonyl, sulfonyl, an oxygen atom, or a sulfur atom; R205 is an alkylene of 1 to 10 carbon atoms, an arylene of 6 to 10 carbon atoms, carbonyl, sulfonyl, an oxygen atom, or a sulfur atom; R206 is hydrogen, a straight or branched alkyl or alkenyl of 1 to 8 carbon atoms, or a hydroxyl-substituted phenyl or naphthyl; R207 is a straight or branched alkylene of 1 to 10 carbon atoms; R208 is hydrogen or hydroxyl; the letter j is an integer from 0 to 5; u and h are each 0 or 1; s, t, sxe2x80x2, txe2x80x2, sxe2x80x3, and txe2x80x3 are each numbers which satisfy s+t=8, sxe2x80x2+txe2x80x2=5, and sxe2x80x3+txe2x80x3=4, and are such that each phenyl skeleton has at least one hydroxyl group; and xcex1 is a number such that the compounds of formula (D8) or (D9) have a molecular weight of from 100 to 1,000.
In the above formulas, suitable examples of R201 and R202 include hydrogen, methyl, ethyl, propyl, butyl, ethynyl, and cyclohexyl; suitable examples of R203 include the same groups as for R201 and R202, as well as xe2x80x94COOH and xe2x80x94CH2COOH; suitable examples of R204 include ethylene, phenylene, carbonyl, sulfonyl, oxygen, and sulfur; suitable examples of R205 include methylene as well as the same groups as for R204; and suitable examples of R206 include hydrogen, methyl, ethyl, propyl, butyl, ethynyl, cyclohexyl, and hydroxyl-substituted phenyl or naphthyl.
Exemplary acid labile groups on the dissolution regulator include groups of the following general formulae (L1) to (L4), tertiary alkyl groups of 4 to 20 carbon atoms, trialkylsilyl groups in which each of the alkyls has 1 to 6 carbon atoms, and oxoalkyl groups of 4 to 20 carbon atoms. 
In these formulas, RL01 and RL02 are each hydrogen or a straight, branched or cyclic alkyl having 1 to 18 carbon atoms; and RL03 is a monovalent hydrocarbon group of 1 to 18 carbon atoms which may contain a heteroatom (e.g., oxygen). A pair of RL01 and RL02, a pair of RL01 and RL03, or a pair of RL02 and RL03 may together form a ring, with the proviso that RL01, RL02, and RL03 are each a straight or branched alkylene of 1 to 18 carbon atoms when they form a ring. RL04 is a tertiary alkyl group of 4 to 20 carbon atoms, a trialkysilyl group in which each of the alkyls has 1 to 6 carbon atoms, an oxoalkyl group of 4 to 20 carbon atoms, or a group of the formula (L1). RL05 is a monovalent hydrocarbon groups of 1 to 8 carbon atoms which may contain a hetero atom or a substituted or unsubstituted aryl group of 6 to 20 carbon atoms. RL06 is a monovalent hydrocarbon groups of 1 to 8 carbon atoms which may contain a hetero atom or a substituted or unsubstituted aryl group of 6 to 20 carbon atoms. RL07 to RL16 independently represent hydrogen or monovalent hydrocarbon groups of 1 to 15 carbon atoms which may contain a hetero atom. Alternatively, RL07 to RL16, taken together, may form a ring. Each of RL07 to RL16 represents a divalent C1-C15 hydrocarbon group which may contain a hetero atom, when they form a ring. Two of RL07 to RL16 which are attached to adjoining carbon atoms may bond together directly to form a double bond. Letter y is an integer of 0 to 6. Letter m is equal to 0 or 1, n is equal to 0, 1, 2 or 3, and 2m+n is equal to 2 or 3. Illustrative examples of these groups are as previously exemplified.
The dissolution regulator may be formulated in an amount of 0 to 50 parts, preferably 0 to 40 parts, and more preferably 0 to 30 parts, per 100 parts of the base resin, and may be used singly or as a mixture of two or more thereof. The use of more than 50 parts would lead to slimming of the patterned film, and thus a decline in resolution.
The dissolution regulator can be synthesized by introducing acid labile groups into a compound having phenolic hydroxyl or carboxyl groups in accordance with an organic chemical formulation.
In the resist composition of the invention, a basic compound may be blended. A suitable basic compound used herein is a compound capable of suppressing the rate of diffusion when the acid generated by the photoacid generator diffuses within the resist film. The inclusion of this type of basic compound holds down the rate of acid diffusion within the resist film, resulting in better resolution. In addition, it suppresses changes in sensitivity following exposure, thus reducing substrate and environment dependence, as well as improving the exposure latitude and the pattern profile.
Examples of basic compounds include primary, secondary, and tertiary aliphatic amines, mixed amines, aromatic amines, heterocyclic amines, carboxyl group-bearing nitrogenous compounds, sulfonyl group-bearing nitrogenous compounds, hydroxyl group-bearing nitrogenous compounds, hydroxyphenyl group-bearing nitrogenous compounds, alcoholic nitrogenous compounds, amide derivatives, and imide derivatives.
Examples of suitable primary aliphatic amines include ammonia, methylamine, ethylamine, n-propylamine, isopropylamine, n-butylamine, iso-butylamine, sec-butylamine, tert-butylamine, pentylamine, tert-amylamine, cyclopentylamine, hexylamine, cyclohexylamine, heptylamine, octylamine, nonylamine, decylamine, dodecylamine, cetylamine, methylenediamine, ethylenediamine, and tetraethylenepentamine. Examples of suitable secondary aliphatic amines include dimethylamine, diethylamine, di-n-propylamine, di-isopropylamine, di-n-butylamine, di-iso-butylamine, di-secbutylamine, dipentylamine, dicyclopentylamine, dihexylamine, dicyclohexylamine, diheptylamine, dioctylamine, dinonylamine, didecylamine, didodecylamine, dicetylamine, N,N-dimethyl-methylenediamine, N,N-dimethylethylenediamine, and N,N-dimethyltetraethylenepentamine. Examples of suitable tertiary aliphatic amines include trimethylamine, triethylamine, tri-n-propylamine, tri-iso-propylamine, tri-n-butylamine, tri-iso-butylamine, tri-sec-butylamine, tripentylamine, tricyclopentylamine, trihexylamine, tricyclohexylamine, triheptylamine, trioctylamine, trinonylamine, tridecylamine, tridodecylamine, tricetylamine, N,N,Nxe2x80x2,Nxe2x80x2-tetramethylmethylenediamine, N,N,Nxe2x80x2,Nxe2x80x2-tetramethylethylenediamine, and N,N,Nxe2x80x2,Nxe2x80x2-tetramethyltetraethylenepentamine.
Examples of suitable mixed amines include dimethylethylamine, methylethylpropylamine, benzylamine, phenethylamine, and benzyldimethylamine. Examples of suitable aromatic and heterocyclic amines include aniline derivatives (e.g., aniline, N-methylaniline, N-ethylaniline, N-propylaniline, N,N-dimethylaniline, 2-methylaniline, 3-methylaniline, 4-methylaniline, ethylaniline, propylaniline, trimethylaniline, 2-nitroaniline, 3-nitroaniline, 4-nitroaniline, 2,4-dinitroaniline, 2,6-dinitroaniline, 3,5-dinitroaniline, and N,N-dimethyltoluidine), diphenyl(p-tolyl)amine, methyldiphenylamine, triphenylamine, phenylenediamine, naphthylamine, diaminonaphthalene, pyrrole derivatives (e.g., pyrrole, 2H-pyrrole, 1-methylpyrrole, 2,4-dimethylpyrrole, 2,5-dimethylpyrrole, and N-methylpyrrole), oxazole derivatives (e.g., oxazole and isooxazole), thiazole derivatives (e.g., thiazole and isothiazole), imidazole derivatives (e.g., imidazole, 4-methylimidazole, and 4-methyl-2-phenylimidazole), pyrazole derivatives, furazan derivatives, pyrroline derivatives (e.g., pyrroline and 2-methyl-1-pyrroline), pyrrolidine derivatives (e.g., pyrrolidine, N-methylpyrrolidine, pyrrolidinone, and N-methylpyrrolidone), imidazoline derivatives, imidazolidine derivatives, pyridine derivatives (e.g., pyridine, methylpyridine, ethylpyridine, propylpyridine, butylpyridine, 4-(1-butylpentyl)pyridine, dimethylpyridine, trimethylpyridine, triethylpyridine, phenylpyridine, 3-methyl-2-phenylpyridine, 4-tert-butyl-pyridine, diphenylpyridine, benzylpyridine, methoxypyridine, butoxypyridine, dimethoxypyridine, 1-methyl-2-pyridine, 4-pyrrolidinopyridine, 1-methyl-4-phenylpyridine, 2-(1-ethyl-propyl)pyridine, aminopyridine, and dimethylaminopyridine), pyridazine derivatives, pyrimidine derivatives, pyrazine derivatives, pyrazoline derivatives, pyrazolidine derivatives, piperidine derivatives, piperazine derivatives, morpholine derivatives, indole derivatives, isoindole derivatives, 1H-indazole derivatives, indoline derivatives, quinoline derivatives (e.g., quinoline and 3-quinoline-carbonitrile), isoquinoline derivatives, cinnoline derivatives, quinazoline derivatives, quinoxaline derivatives, phthalazine derivatives, purine derivatives, pteridine derivatives, carbazole derivatives, phenanthridine derivatives, acridine derivatives, phenazine derivatives, 1,10-phenanthroline derivatives, adenine derivatives, adenosine derivatives, guanine derivatives, guanosine derivatives, uracil derivatives, and uridine derivatives.
Examples of suitable carboxyl group-bearing nitrogenous compounds include aminobenzoic acid, indolecarboxylic acid, and amino acid derivatives (e.g. nicotinic acid, alanine, alginine, aspartic acid, glutamic acid, glycine, histidine, isoleucine, glycylleucine, leucine, methionine, phenylalanine, threonine, lysine, 3-amino-pyrazine-2-carboxylic acid, and methoxyalanine). Examples of suitable sulfonyl group-bearing nitrogenous compounds include 3-pyridinesulfonic acid and pyridinium p-toluenesulfonate. Examples of suitable hydroxyl group-bearing nitrogenous compounds, hydroxyphenyl group-bearing nitrogenous compounds, and alcoholic nitrogenous compounds include 2-hydroxypyridine, aminocresol, 2,4-quinolinediol, 3-indolemethanol hydrate, monoethanolamine, diethanolamine, triethanolamine, N-ethyldiethanolamine, N,N-diethylethanol-amine, triisopropanolamine, 2,2xe2x80x2-iminodiethanol, 2-amino-ethanol, 3-amino-1-propanol, 4-amino-1-butanol, 4-(2-hydroxyethyl)morpholine, 2-(2-hydroxyethyl)pyridine, 1-(2-hydroxyethyl)piperazine, 1-[2-(2-hydroxyethoxy)ethyl]-piperazine, piperidine ethanol, 1-(2-hydroxyethyl)-pyrrolidine, 1-(2-hydroxyethyl)-2-pyrrolidinone, 3-piperidino-1,2-propanediol, 3-pyrrolidino-1,2-propanediol, 8-hydroxyjulolidine, 3-quinuclidinol, 3-tropanol, 1-methyl-2-pyrrolidine ethanol, 1-aziridine ethanol, N-(2-hydroxy-ethyl)phthalimide, and N-(2-hydroxyethyl)isonicotinamide. Examples of suitable amide derivatives include formamide, N-methylformamide, N,N-dimethylformamide, acetamide, N-methyl-acetamide, N,N-dimethylacetamide, propionamide, and benzamide. Suitable imide derivatives include phthalimide, succinimide, and maleimide.
In addition, basic compounds of the following general formula (B1) may also be included alone or in admixture.
N(X)n(Y)3-nxe2x80x83xe2x80x83(B1)
In the formula, n is equal to 1, 2 or 3; side chain Y is independently hydrogen or a straight, branched or cyclic alkyl group of 1 to 20 carbon atoms which may contain a hydroxyl group or ether; and side chain X is independently selected from groups of the following general formulas (X1) to (X3), and two or three X""s may bond together to form a ring. 
In the formulas, R300, R302 and R305 are independently straight or branched alkylene groups of 1 to 4 carbon atoms; R301 and R304 are independently hydrogen, straight, branched or cyclic alkyl groups of 1 to 20 carbon atoms, which may contain at least one hydroxyl group, ether, ester or lactone ring; R303 is a single bond or a straight or branched alkylene group of 1 to 4 carbon atoms; and R306 is a single bond or a straight, branched or cyclic alkyl group of 1 to 20 carbon atoms which may contain one or more hydroxyl groups, ether groups, ester groups or lactone rings.
Illustrative examples of the compounds of formula (B1) include tris(2-methoxymethoxyethyl)amine, tris{2-(methoxyethoxy)ethyl}-amine, tris{2-(2-methoxyethoxymethoxy)ethyl}-amine, tris(2-(1-methoxyethoxy)ethyl)amine, tris(2-(1-ethoxyethoxy)ethyl)}amine, tris{2-(1-ethoxypropoxy)ethyl}amine, tris[2-{2-(2-hydroxyethoxy)ethoxy}ethyl]amine, 4,7,13,16,21,24-hexaoxa-1,10-diazabicyclo[8.8.8]hexacosane, 4,7,13,18-tetraoxa-1,10-diazabicyclo[8.5.5]eicosane, 1,4,10,13-tetraoxa-7,16-diazabicyclooctadecane, 1-aza-12-crown-4, 1-aza-15-crown-5, 1-aza-18-crown-6, tris(2-formyloxyethyl)amine, tris(2-acetoxyethyl)amine, tris(2-propionyloxyethyl)amine, tris(2-butyryloxyethyl)amine, tris(2-isobutyryloxyethyl)amine, tris(2-valeryloxyethyl)-amine, tris(2-pivaloyloxyethyl)amine, N,N-bis(2-acetoxy-ethyl)-2-(acetoxyacetoxy)ethylamine, tris(2-methoxycarbonyl-oxyethyl)amine, tris(2-tert-butoxycarbonyloxyethyl)amine, tris[2-(2-oxopropoxy)ethyl]amine, tris[2-(methoxycarbonyl-methyl)oxyethyl]amine, tris[2-(tert-butoxycarbonylmethyl-oxy)ethyl]amine, tris[2-(cyclohexyloxycarbonylmethyloxy)-ethyl]amine, tris(2-methoxycarbonylethyl)amine, tris(2-ethoxycarbonylethyl)amine, N,N-bis(2-hydroxyethyl)-2-(methoxycarbonyl)ethylamine, N,N-bis(2-acetoxyethyl)-2-(methoxycarbonyl)ethylamine, N,N-bis(2-hydroxyethyl)-2-(ethoxycarbonyl)ethylamine, N,N-bis(2-acetoxyethyl)-2-(ethoxycarbonyl)ethylamine, N,N-bis(2-hydroxyethyl)-2-(2-methoxyethoxycarbonyl)ethylamine, N,N-bis(2-acetoxyethyl)-2-(2-methoxyethoxycarbonyl)ethylamine, N,N-bis(2-hydroxy-ethyl)-2-(2-hydroxyethoxycarbonyl)ethylamine, N,N-bis(2-acetoxyethyl)-2-(2-acetoxyethoxycarbonyl)ethylamine, N,N-bis(2-hydroxyethyl)-2-[(methoxycarbonyl)methoxycarbonyl]-ethylamine, N,N-bis(2-acetoxyethyl)-2-[(methoxycarbonyl)-methoxycarbonyl]-ethylamine, N,N-bis(2-hydroxyethyl)-2-(2-oxopropoxycarbonyl)ethylamine, N,N-bis(2-acetoxyethyl)-2-(2-oxopropoxycarbonyl)ethylamine, N,N-bis(2-hydroxyethyl)-2-(tetrahydrofurfuryloxycarbonyl)ethylamine, N,N-bis(2-acetoxyethyl)-2-(tetrahydrofurfuryloxycarbonyl)ethylamine, N,N-bis(2-hydroxyethyl)-2-[(2-oxotetrahydrofuran-3-yl)oxy-carbonyl]ethylamine, N,N-bis(2-acetoxyethyl)-2-[(2-oxotetrahydrofuran-3-yl)oxycarbonyl]ethylamine, N,N-bis(2-hydroxy-ethyl)-2-(4-hydroxybutoxycarbonyl)ethylamine, N,N-bis(2-formyloxyethyl)-2-(4-formyloxybutoxycarbonyl)ethylamine, N,N-bis(2-formyloxyethyl)-2-(2-formyloxyethoxycarbonyl)-ethylamine, N,N-bis(2-methoxyethyl)-2-(methoxycarbonyl)-ethylamine, N-(2-hydroxyethyl)-bis[2-(methoxycarbonyl)-ethyl]amine, N-(2-acetoxyethyl)-bis[2-(methoxycarbonyl)-ethyl]amine, N-(2-hydroxyethyl)-bis[2-(ethoxycarbonyl)-ethyl]amine, N-(2-acetoxyethyl)-bis[2-(ethoxycarbonyl)-ethyl]amine, N-(3-hydroxy-1-propyl)-bis[2-(methoxycarbonyl)-ethyl]amine, N-(3-acetoxy-1-propyl)-bis[2-(methoxycarbonyl)-ethyl]amine, N-(2-methoxyethyl)-bis[2-(methoxycarbonyl)-ethyl]amine, N-butyl-bis[2-(methoxycarbonyl)ethyl]amine, N-butyl-bis[2-(2-methoxyethoxycarbonyl)ethyl]amine, N-methyl-bis(2-acetoxyethyl)amine, N-ethyl-bis(2-acetoxyethyl)amine, N-methyl-bis(2-pivaloyloxyethyl)amine, N-ethyl-bis[2-(methoxycarbonyloxy)ethyl]amine, N-ethyl-bis[2-(tert-butoxy-carbonyloxy)ethyl]amine, tris(methoxycarbonylmethyl)amine, tris(ethoxycarbonylmethyl)amine, N-butyl-bis(methoxy-carbonylmethyl)amine, N-hexyl-bis(methoxycarbonylmethyl)-amine, and xcex2-(diethylamino)-xcex4-valerolactone.
The basic compound is preferably formulated in an amount of 0.001 to 10 parts, and especially 0.01 to 1 part, per part of the photoacid generator. Less than 0.001 part of the basic compound may fail to achieve the desired effects thereof, while the use of more than 10 parts would result in too low a sensitivity and resolution.
In the resist composition, a compound bearing a xe2x89xa1Cxe2x80x94COOH group in a molecule may be blended. Exemplary, non-limiting compounds bearing a xe2x89xa1Cxe2x80x94COOH group include one or more compounds selected from Groups I and II below. Including this compound improves the PED stability of the resist and ameliorates edge roughness on nitride film substrates.
Compounds in which some or all of the hydrogen atoms on the phenolic hydroxyl groups of the compounds of general formulas (A1) to (A10) below have been replaced with xe2x80x94R401xe2x80x94COOH (wherein R401 is a straight or branched alkylene of 1 to carbon atoms), and in which the molar ratio C/(C+D) of phenolic hydroxyl groups (C) to xe2x89xa1Cxe2x80x94COOH groups (D) in the molecule is from 0.1 to 1.0.
In these formulas, R408 is hydrogen or methyl; R402 and R403 are each hydrogen or a straight or branched alkyl or alkenyl of 1 to 8 carbon atoms; R404 is hydrogen, a straight or branched alkyl or alkenyl of 1 to 8 carbon atoms, or a xe2x80x94(R409)hxe2x80x94COORxe2x80x2 group (Rxe2x80x2 being hydrogen or xe2x80x94R409xe2x80x94COOH); R405 is xe2x80x94(CH2)ixe2x80x94 (wherein i is 2 to 10), an arylene of 6 to 10 carbon atoms, carbonyl, sulfonyl, an oxygen atom, or a sulfur atom; R406 is an alkylene of 1 to 10 carbon atoms, an arylene of 6 to 10 carbon atoms, carbonyl, sulfonyl, an oxygen atom, or a sulfur atom; R407 is hydrogen, a straight or branched alkyl or alkenyl of 1 to 8 carbon atoms, or a hydroxyl-substituted phenyl or naphthyl; R409 is a straight or branched alkylene of 1 to 10 carbon atoms; R410 is hydrogen, a straight or branched alkyl or alkenyl of 1 to 8 carbon atoms, or a xe2x80x94R411xe2x80x94COOH group; R411 is a straight or branched alkylene of 1 to carbon atoms; the letter j is an integer from 0 to 5; u and h are each 0 or 1; s1, t1, s2, t2, s3, t3, s4, and t4 are each numbers which satisfy s1+t1=8, s2+t2=5, s3+t3=4, and s4+t4=6, and are such that each phenyl skeleton has at least one hydroxyl group; xcexa is a number such that the compound of formula (A6) may have a weight average molecular weight of 1,000 to 5,000; and xcex is a number such that the compound of formula (A7) may have a weight average molecular weight of 1,000 to 10,000.
Compounds of general formulas (A11) to (A15) below. 
In these formulas, R402, R403, and R411 are as defined above; R412 is hydrogen or hydroxyl; s5 and t5 are numbers which satisfy s5xe2x89xa70, t5xe2x89xa70, and s5+t5=5; and hxe2x80x2 is equal to 0 or 1.
Illustrative, non-limiting examples of the compound bearing a xe2x89xa1Cxe2x80x94COOH group include compounds of the general formulas AI-1 to AI-14 and AII-1 to AII-10 below. 
In the above formulas, Rxe2x80x3 is hydrogen or a CH2COOH group such that the CH2COOH group accounts for 10 to 100 mol % of Rxe2x80x3 in each compound, xcex1 and xcexa are as defined above. 
The compound bearing a xe2x89xa1Cxe2x80x94COOH group within the molecule may be used singly or as combinations of two or more thereof.
The compound bearing a xe2x89xa1Cxe2x80x94COOH group within the molecule is added in an amount ranging from 0 to 5 parts, preferably 0.1 to 5 parts, more preferably 0.1 to 3 parts, further preferably 0.1 to 2 parts, per 100 parts of the base resin. More than 5 parts of the compound can reduce the resolution of the resist composition.
The resist composition of the invention may additionally include an acetylene alcohol derivative for the purpose of enhancing the shelf stability. Preferred acetylene alcohol derivatives are those having the general formula (Si) or (S2) below. 
In the formulas, R501, R502, R503 R504 and R505 are each hydrogen or a straight, branched, or cyclic alkyl of 1 to 8 carbon atoms; and X and Y are each 0 or a positive number, satisfying 0xe2x89xa6Xxe2x89xa630, 0xe2x89xa6Yxe2x89xa630, and 0xe2x89xa6X+Yxe2x89xa640.
Preferable examples of the acetylene alcohol derivative include Surfynol 61, Surfynol 82, Surfynol 104, Surfynol 104E, Surfynol 104H, Surfynol 104A, Surfynol TG, Surfynol PC, Surfynol 440, Surfynol 465, and Surfynol 485 from Air Products and Chemicals Inc., and Surfynol E1004 from Nisshin Chemical Industry K.K.
The acetylene alcohol derivative is preferably added in an amount of 0.01 to 2% by weight, and more preferably 0.02 to 1% by weight, per 100% by weight of the resist composition. Less than 0.01% by weight would be ineffective for improving coating characteristics and shelf stability, whereas more than 2% by weight would result in a resist having a low resolution.
The resist composition of the invention may include, as an optional ingredient, a surfactant which is commonly used for improving the coating characteristics. Optional ingredients may be added in conventional amounts so long as this does not compromise the objects of the invention.
Nonionic surfactants are preferred, examples of which include perfluoroalkylpolyoxyethylene ethanols, fluorinated alkyl esters, perfluoroalkylamine oxides, perfluoroalkyl EO-addition products, and fluorinated organosiloxane compounds. Useful surfactants are commercially available under the trade names Florade FC-430 and FC-431 from Sumitomo 3M Co., Ltd., Surflon S-141 and S-145 from Asahi Glass Co., Ltd., Unidyne DS-401, DS-403 and DS-451 from Daikin Industries Ltd., Megaface F-8151 from Dai-Nippon Ink and Chemicals Inc., and X-70-092 and X-70-093 from Shin-Etsu Chemical Co., Ltd. Preferred surfactants are Florade FC-430 from Sumitomo 3M and X-70-093 from Shin-Etsu Chemical Co., Ltd.
Pattern formation using the resist composition of the invention may be carried out by a known lithographic technique. For example, the resist composition is applied onto a substrate such as a silicon wafer by spin coating or the like to form a resist film having a thickness of 0.2 to 2.0 xcexcm, which is then pre-baked on a hot plate at 60 to 150xc2x0 C. for 1 to 10 minutes, and preferably at 80 to 130xc2x0 C. for 1 to 5 minutes. A patterning mask having the desired pattern is then placed over the resist film, and the film exposed through the mask to an electron beam or to high-energy radiation such as deep-UV rays, excimer laser beams or x-rays in a dose of about 1 to 200 mJ/cm2, and preferably about 5 to 100 mJ/cm2, then post-exposure baked (PEB) on a hot plate at 60 to 150xc2x0 C. for 1 to 5 minutes, and preferably at 80 to 130xc2x0 C. for 1 to 3 minutes. Finally, development is carried out using as the developer an aqueous alkali solution, such as a 0.1 to 5% (preferably 2 to 3%) aqueous solution of tetramethylammonium hydroxide (TMAH), this being done by a conventional method such as dipping, puddling, or spraying for a period of 0.1 to 3 minutes, and preferably 0.5 to 2 minutes. These steps result in the formation of the desired pattern on the substrate. Of the various types of high-energy radiation that may be used, the resist composition of the invention is best suited to fine pattern formation with, in particular, deep-UV rays having a wavelength of 248 to 193 nm, excimer laser beams, x-rays, or electron beams. The desired pattern may not be obtainable outside the upper and lower limits of the above range.
The resist composition comprising the polymer as a base resin lends itself to micropatterning with electron beams or deep-UV rays since it is sensitive to high-energy radiation and has excellent sensitivity, resolution, and etching resistance. Especially because of the minimized absorption at the exposure wavelength of an ArF or KrF excimer laser, a finely defined pattern having sidewalls perpendicular to the substrate can easily be formed.